One strikeout, one hit against low-grade serous carcinomas

Two MEK inhibitors were tested against recurrent low-grade serous carcinomas of the ovaries, fallopian tubes, or peritoneum, but only one inhibitor offered clinical benefit over standard care, investigators from two randomized trials reported.

In a phase 2/3 trial, the median PFS was 13 months for patients treated with trametinib and 7.2 months for patients who received an aromatase inhibitor or chemotherapy (P < .0001).

“Our findings suggest that trametinib represents a new standard-of-care treatment option for women with recurrent low-grade serous carcinoma,” said investigator David M. Gershenson, MD, of the University of Texas MD Anderson Cancer Center in Houston.

In contrast, in the phase 3 MILO/ENGOT-ov11 trial, there was no significant difference in PFS between patients treated with binimetinib and those who received physician’s choice of chemotherapy. The median PFS was 11.2 months with binimetinib and 14.1 months with chemotherapy (P = .752).

“Although this study did not meet its primary endpoint, binimetinib showed activity in low-grade serous ovarian cancer across the efficacy endpoints evaluated, with a response rate of 24% and a median PFS of 11.2 months on updated analysis. Chemotherapy responses were better than predicted, based on historical retrospective data,” said investigator Rachel N. Grisham, MD, of Memorial Sloan Kettering Cancer Center in New York.

Chemoresistant cancers

Low-grade serous ovarian or peritoneal cancers are rare, accounting for only 5% to 10% of all serous cancers, Dr. Gershenson noted.

“[Low-grade serous cancers are] characterized by alterations in the MAP kinase pathway, as well as relative chemoresistance, and prolonged overall survival compared to high-grade serous cancers. Because of this subtype’s relative chemoresistance, the search for novel therapeutics has predominated over the last decade or so,” he said.

MEK inhibitors interfere with the MEK1 and MEK2 enzymes in the MAPK pathway. Alterations in MAPK, especially in KRAS and BRAF proteins, are found in 30%-60% of low-grade serous carcinomas, providing the rationale for MEK inhibitors in these rare malignancies.

Standard care consisted of one of the following: letrozole at 2.5 mg daily; pegylated liposomal doxorubicin at 40-50 mg IV every 28 days; weekly paclitaxel at 80 mg/m2 for 3 out of 4 weeks; tamoxifen at 20 mg twice daily; or topotecan at 4 mg/m2 on days 1, 8, and 15 every 28 days. Patients randomized to standard care could be crossed over to trametinib at progression.

All patients had at least one prior line of platinum-based chemotherapy, and nearly half had three or more prior lines of therapy. The median age was 56.6 years in the trametinib arm and 55.3 years in the control arm.

At a median follow-up of 31.4 months, median PFS, the primary endpoint, was 13 months with trametinib vs. 7.2 months with standard care. The hazard ratio (HR) for progression on trametinib was 0.48 (P < .0001).

The overall response rates were 26.2% in the trametinib arm and 6.2% in the standard care arm. The odds ratio for response on trametinib was 5.4 (P < .0001).

For 88 patients who crossed over to trametinib, the median PFS was 10.8 months, and the overall response rate was 15%.

Trametinib was also associated with a significantly longer response duration, at a median of 13.6 months, compared with 5.9 months for standard care (P value not shown).

The median overall survival was 37 months with trametinib and 29.2 months with standard care, with an HR favoring trametinib of 0.75, although this just missed statistical significance (P = .054). Dr. Gershenson pointed out that the overall survival in the standard care arm included patients who had been crossed over to trametinib.

Grade 3 or greater adverse events included hematologic toxicities in 13.4% of patients on trametinib and 9.4% on standard care; gastrointestinal toxicity in 27.6% and 29%, respectively; skin toxicities in 15% and 3.9%, respectively; and vascular toxicities in 18.9% and 8.6%, respectively.